Perl-Toolchain-Gang/Module-Build — comment on commit 886abd6b50511cc3183162817cae0fdfa18f060f
File:  line 0
By Leont:

> So, I think the current precedence is: command line arguments, PERL_MB_OPT arguments, modulebuildrc arguments (for a given action), then cached Build.PL settings. (But it's been a while since I reviewed the hash merging code.)

That seems to be correct, but it should be realized that *the cached Build.PL settings* is apparently not just the arguments to Build.PL, but also PERL_MB_OPT arguments and the Build_PL modulebuildrc arguments (in that order). So PERL_MB_OPT is handled twice, and Build_PL configuration is a lowest precedence catch-all; both of these are rather surprising to me, and possibly problematic (e.g. if an option is not idempotent).